Hazelcast MapStoreConfig ignored

Question

I'm using a map store to persist my hazelcast distributed map in a database.

In my test case, I start three hazelcast instances, each configured the same way:

Config cfg = new Config();
cfg.setInstanceName("name");
hazelcast = Hazelcast.newHazelcastInstance(cfg);    
MapConfig mapConfig = new MapConfig("myMapName");
MapStoreConfig mapStoreConfig = new MapStoreConfig();
mapStoreConfig.setClassName(MyMapStore.class.getName());
mapStoreConfig.setWriteDelaySeconds(0);
mapStoreConfig.setEnabled(true);
mapConfig.setMapStoreConfig(mapStoreConfig);
mapConfig.setBackupCount(2);
hazelcast.getConfig().addMapConfig(mapConfig);
IMap myMap = hazelcast.getMap("myMapName");

However, when I add values to the map, only the first Cluster member writes into the database, the MapStoreConfig is just set to Default values on each other node. But, if I change the code to the following, it works:

Config cfg = new Config();
cfg.setInstanceName("name");
MapConfig mapConfig = new MapConfig("myMapName");
MapStoreConfig mapStoreConfig = new MapStoreConfig();
mapStoreConfig.setClassName(MyMapStore.class.getName());
mapStoreConfig.setWriteDelaySeconds(0);
mapStoreConfig.setEnabled(true);
mapConfig.setMapStoreConfig(mapStoreConfig);
mapConfig.setBackupCount(2);
cfg.addMapConfig(mapConfig);
hazelcast = Hazelcast.newHazelcastInstance(cfg);
IMap myMap = hazelcast.getMap("myMapName");

Seems like the line hazelcast.getConfig().addMapConfig(mapConfig); is ignored. Tested with hazelcast v3.1.5.

Marco13 Marco13 · Accepted Answer · 2014-01-27T12:21:09

To my understanding, the Config instance should be considered only as a sort of "template", which is used to create one instance, but may not be used to afterwards modify this instance. Although, according to a quick websearch and a look at the documentation, this is not stated explicitly, but

all examples that I have seen so far follow the pattern of FIRST creating and the complete Config, and THEN creating the corresponding instance and
the addMapConfig method (in https://github.com/hazelcast/hazelcast/blob/master/hazelcast/src/main/java/com/hazelcast/config/Config.java ) does not involve any notification mechanism. So there would at least have to be some mechanism to inform the Hazelcast instance about the changed config, but I think that such a mechanism does not exist.

From what I have read in the source code ( e.g. in https://github.com/hazelcast/hazelcast/blob/master/hazelcast/src/main/java/com/hazelcast/instance/Node.java and https://github.com/hazelcast/hazelcast/blob/master/hazelcast/src/main/java/com/hazelcast/instance/HazelcastInstanceImpl.java ), the Config is only read at construction time, and it does not seem to be possible to change the configuration after the Hazelcast instance has been created.

Hazelcast MapStoreConfig ignored

2 Answers